Intra Operative Neuro Monitoring (IONM)

Question 1

How is an electroencephalogram (EEG) used for intraoperative monitoring and diagnosis?

Answer 1

• monitors CNS function and ischemia
• burst suppression
• depth of anesthesia

Question 2

What happen to the EEG waves during ischemia?

Answer 2

A progressive reduction in CBF will produce a reliable pattern change in the EEG

• loss of high frequency activity
• loss of power
• eventual progression to EEG silence

Question 3

What is cerebral oximetry?

Answer 3

Noninvasive cerebral oxygenation measurement using near infrared spectroscopy (NIRS) technology

Question 4

When is cerebral oximetry used?

Answer 4

Any procedure where there may be vascular compromise to the brain from restriction of blood flow or patient positioning

Question 5

During cerebral oximetry, what measurement is significant?

Answer 5

A decrease of 20% from baseline

Question 6

In conjunction with standard monitors, what other monitor is used to measure depth of anesthesia?

Answer 6

The BIS monitor

Question 7

What do 0, 20,40,60 80 and 100 represent on a BIS monitor?

Answer 7

0 = flatline EEG
0-20 = burst suppression
20-40= deep hypnotic state
40-60 = general anesthesia
     - low probability of explicit recall. 
     - unresponsive to verbal stimulus
60-80 = responds to loud command or mild prodding/shaking
80-100 = awake- responds to normal voice

Question 8

What do evoked potential modalities detect?

Answer 8

Signals that are the results of specific stimuli applied to the patient

Question 9

What are the different types of evoked potentials?

Answer 9

Somatosensory evoked potential SSEP
Brainstem auditory evoked potential BAEP
Visual evoked potential. VEP
Motor evoked potential. MEP

Question 10

What is the proposed benefit of EP monitoring?

Answer 10

To identify the deterioration of neuronal function in order to provide opportunity to correct offending factors before they are irreversible.

Question 11

During EP monitoring, what are potential offending factors?

Answer 11

• position of the patient
• hypotension
• hypothermia
• surgical intervention

Question 12

What is an SSEP?

Answer 12

• A signal that is detectable on EEG monitoring the primary somatosensory cortex
• generated by a cutaneous electrical stimulation of a peripheral sensory nerve or a cranial nerve with a sensory pathway

Question 13

How is SSEP described?

Answer 13

Described by:

• Polarity: direction of wave deflection
• latency: time required for a signal to be detected after a stimulus has been applied

Question 14

What is an SSEP quantified by?

Answer 14

Quantified by:

• amplitude of the resulting signal
• latency of the resulting signal

Question 15

During SSEP monitoring, _________ _________ is more common than mechanical disruptive change.

Answer 15

Ischemic change

Question 16

During SSEP, ischemia causes ____________ of the signal to decrease and the ___________ of the signal to increase.

Answer 16

Amplitude

Latency

Question 17

What are clinically significant SSEP wave changes?

Answer 17

• 50% decrease in signal amplitude

- 10% increase in signal latency

Question 18

How is Motor evoke potential (MEP) different from other EP modalities?

Answer 18

It evaluates descending motor pathways

Question 19

_____ acts as a complement to SSEP, particularly in the setting of _______ _________.

Answer 19

MEP

Spine surgery

Question 20

What does using both SSEP and MEP monitoring during spine surgery provide?

Answer 20

Information about the integrity of anatomically different areas of the spinal cord.

Question 21

What happens to elicit an MEP?

Answer 21

• A stimulus is applied in a transcranial fashion over the motor cortex
• the deflection, essentially an electomyographic signal, is then detected by electrodes embedded in the muscle belly

Question 22

Transcranial electrical stimulus is usually delivered as a _____ ___________________, the voltage is then adjusted to achieve adequate signals in both the ________ and _______ extremities.

Answer 22

Rapid train of four or more stimuli
Upper
Lower

Question 23

Which agents have more depressant effects on EP monitoring?

Answer 23

Inhalation agents, including nitrous oxide generally have more depressant effects than IV agents

Question 24

T/F volatile agents can have a profound influence on the amplitude and latency of evoked potentials.

Answer 24

True

Question 25

EP signals can be obtainable under volatile anesthesia. How is this achieved?

Answer 25

Keeping the anesthetic at sub-MAC doses to avoid degradation in quality of the signals

Question 26

What do Propofol and Thiopental do to EPs?

Answer 26

Attenuate the amplitude of all modalities of EP, but do not obliterate them

Question 27

What do ketamine and Etomidate do to SSEPs?

Answer 27

Enhance the quality of SSEP signals in patients with a weak baseline, although clinical significance remains unclear

Question 28

What effects to opioids, benzos, and precedex have on EPs?

Answer 28

Negligible effects on recording of EP

Question 29

MEP are exquisitely sensitive to the ___________ effects of _______ ________, including nitrous oxide.

Answer 29

Depressant

Inhalation anesthetics

Question 30

What is the ideal anesthesia for monitoring MEP?

Answer 30

TIVA without nitrous oxide

Question 31

Monitoring of MEP generally precludes the use of ____________.

Answer 31

Paralytics

Question 32

MEP can cause ______ __________, so MEP signals are typically obtained intermittently at points during surgery.

Answer 32

Patient movement

Question 33

What is mandatory to prevent injury to the tongue during transcranial stimulation?

Answer 33

A bite block